In general, the invention features DNA-protein fusions and their uses, particularly for the selection of desired proteins and their corresponding nucleic acid sequences.
Recently, a combinatorial method was developed for the isolation of proteins with desired properties from large pools of proteins (Szostak et al., U.S. Ser. No. 09/007,005; Szostak et al., WO98/31700; Roberts & Szostak, Proc. Natl. Acad. Sci. USA (1997) vol. 94, p. 12297–12302). By this method, the protein portion is linked to its encoding RNA by a covalent chemical bond. Due to the covalent nature of this linkage, selection experiments are not limited to the extremely mild reaction conditions that must be used for approaches that involve non-covalent complex formation such as ribosome display (Hanes & Plückthun, Proc. Natl. Acad. Sci. USA (1997) vol. 94, p. 4937–4942; He & Taussig, Nucl. Acids Res. (1997) vol. 25, p 5132–5143). However, precautions do need to be taken during the selection process to minimize RNA degradation, since the accidental cleavage of ribo-bonds can result in the irreversible loss of encoded information. For this reason, these selection procedures are typically carried out using reaction media and equipment that are free of ribonucleases or other deleterious contaminants.